Dsquared2 interview: Double vision

Twins Dean and Dan Caten do everything together: they work together, party together – even share a bedroom. And now the fashion designers behind DSquared2 plan to spread the love: their democratic vision, loved by the A-list, is coming our way

Two of a kind: Dean and Dan Caten at home in London. Photograph: Pal Hansen for the Observer

I have been sitting in Dean and Dan Caten's kitchen, just off Portobello Road, for 20 minutes when they burst into the room. "We're so sorry we're late!" they trill in unison, holding out perfectly tanned, perfectly manicured hands, as they both flash the whitest, most expensive looking sets of teeth I've ever seen. The twins trot around like two highly groomed show ponies, offering drinks and yakking away about their "dramatic" visit to the Brazilian embassy earlier in the day – they're off to South America on an "inspiration trip" soon and they'd forgotten to sort out their visas.

"I think," announces Dean, "we should have champagne!" It's 3pm on a weekday afternoon and the room falls momentarily silent. All of us are mentally calculating whether this is a good idea. "Dean," Dan says, sternly, "we'll all have mineral water." Dean looks a little crestfallen. "He's the naughty one," Dan explains, raising an eyebrow in Dean's direction just as he lights what will be the first of several cigarettes of the afternoon. "Yes, I'm the bad one," Dean agrees, exhaling. "Well, you can't have day without night, good without evil or… fat without skinny!"

I'm here to talk to the Canadian fashion designers about their multi-million-pound fashion empire, DSquared2, which has practically cornered the market in what Women's Wear Daily, the fashion-industry bible, refers to as "va-va-voom sex appeal". They have dressed everyone from Kanye West and Justin Bieber to George Clooney on the red carpet, designed stage-tour wardrobes for Britney Spears and Madonna, and had their "beautiful friend" Rihanna, among other stars, appear in their outrageously fun catwalk shows (for Spring/Summer 2012, their inspiration was Glastonbury, so they sent models down the catwalk trawling through five inches of mud).

They're "super-excited" about a promotional video that they're due to shoot: "It'll be school-themed. And we'll be starring in it," says Dan, as Dean nods in agreement. "And the budget is humongous. We're going to be playing supply teachers and we'll be wearing high heels. We wanted to make the music, too – have the number one summer hit we've always dreamed of. Why not? If musicians think they can be designers, then why can't we be musicians? The whole thing is going to be very DSquared2-ey."

The Catens, aged 47 ("Hell-ooo, can you believe it?"), were born and raised in Toronto by their English mother and Italian father, a welder who emigrated to Canada and shortened his surname from Catenacci to Caten to "blend in" to his new life. The family wasn't well off, and the twins, as they were inevitably known, were the youngest of nine children. They grew up at home with the two sisters directly older than them – the rest of their siblings had moved out by the time they were old enough to notice – "but they all influenced us in some way: some sisters were disco queens, our brothers were rockers, and we had a few granolas [hippies] in the family, too," says Dan.

Life for the youngest Catens, Dan says, was a case of "us against the world" and, he continues, "it's always been that way. A woman once told us we shared the same soul and we think that's true."

Have you ever spent time apart, I ask.

"No, we do everything together," says Dean. They look at each other knowingly and Dean lets out a sigh: "Well, we were separated for six months when we were 16. It was horrible."

Why were you separated?

There's an uncomfortable pause. Dan eventually breaks the silence. "We don't really want to talk about it. But let's just say that Dean was bad and got sent away for a while. It's the only time we've ever been apart. Anyway, let's talk about hopes and dreams instead!"

The Catens's "hopes and dreams" had always been in fashion. Leaving Toronto at 19, they moved to New York to study fashion at Parsons School for Design. They dropped out after one semester, deeming that it "wasn't for them" and returned to Toronto, where they were employed as junior designers by Canadian label Ports International. "We had a great, great mentor there. He taught us how important the height of the breast pocket should be. The cut of the collar… he really believed in us when no one else did," says Dean. There, they worked their way up to the position of joint head designers, before moving to Milan in 1991. "We came full circle. We were proud of our Italian roots and wanted to go and see what it was all about," says Dan.

It was in Italy, after securing financial backing from Renzo Rosso – the founder and president of fashion brand Diesel – that the Catens launched DSquared2 in 1992. It was conceived as a premium denim label: think of the well-cut, super-expensive distressed denim that was all the rage in the early noughties when people had money to burn, a look much loved by wealthy Italians and young, off-duty stockbrokers. It did well – so well, in fact, that DSquared2 was able to expand and move on to what the twins "really wanted to do", which was to design men's and womenswear.

Their first menswear collection launched in 1994, and in 2003 they launched their inaugural women's collection (where supermodels descended from a pink aeroplane on to the catwalk). They have since diversified: the pricey jeans and slogan T-shirts are still there, the backbone in a portfolio that spans fragrances, sunglasses, accessories and, most recently, handbags. Turnover last year was £116m: that's an increase of 10% from 2010, so it's fair to say that the economic cloud hasn't descended on the Catens.

Is there anything else they have their sights set on? "We're control freaks," says Dean. "We have to put our noses in everything. We don't just want our name slapped on stuff to make a profit." Dan continues: "But we'd love to become household names: homeware and baby clothes and anything we like." Baby clothes? "Yeah, it's cute." Dean then adds, "We're not those types of conceptual designers. We make things we like, that our customers like, and that people actually wear. There's loads of other designers who do that other thing. To us, it's fashion: it's not reinventing the wheel, we're just trying to make it roll a little better."

Before I go, the Catens show me around their London house; we walk down a hallway lined with their latest campaign shots, model Lara Stone stares down sexily from gilt frames. "And this," Dean chirrups, "is our bedroom." You share a room? "Yes, of course!" "But you're 47!" I say. They both look a little shocked at my reaction. "We sleep in the same bed – we always have. We just lie in bed blabbing until one of us falls asleep. Unless one of us has a special guest, of course," he says, motioning to the second bedroom down the hall.

As I walk out of their front door, I turn to them and say, "You really mean it when you say you do everything together, don't you?" They both nod: "We feel things between each other, so we have to do everything together. If something were to happen to one of us… I mean if one of us was in an accident…" Dan trails off. Dean finishes for him: "We came into the world together and we're leaving together. There will never be just one of us. But anyway, let's talk more about hopes and dreams!"